A dye is defined herein as a material lending visible color when dissolved in the dyed product. Examples of dyes which have been used for dyeing organic liquids are Color Index Solvent Red #24, Solvent Red #19, Solvent Yellow #14, Solvent Blue #36, and Solvent Green #3.
A marker is defined herein as a substance which can be dissolved in a liquid to be identified then subsequently detected by performing a simple chemical or physical test on the marked liquid. Markers that have been proposed, or are in use, include furfural, quinizarin, diphenylamine and radioactive materials. (Radioactive materials have not been accepted in Western countries because of special equipment and precautionary measures associated with their handling.)
Dyes and markers (referred to collectively as "tags" herein) are needed to clearly distinguish chemically or physically similar liquids. As one example, fuels are dyed to provide visually distinctive brand and grade denominations for commercial and safety reasons. As another example, some lightly taxed products are tagged to distinguish them from similar materials subject to higher taxes. Furthermore, certain fuels are dyed or marked to deter fraudulent adulteration of premium grade products with lower grade products, such as by blending kerosene, stove oil, or diesel fuel into regular grade gasoline or blending regular grade gasoline into premium grade gasoline. Identification of particular batches of bulk liquids for protection against theft is another valuable function of markers and dyes, particularly for identifying fuels owned by large government, military or commercial consumers. Finally, marketers of brand name products tag their products with dyes or markers to detect substitution of others' products in their distribution system.
Dyes alone are not always adequate to securely and reliably tag liquids. Many dyes are easily removed by unauthorized persons. Furthermore, dyes can be obscured by other natural or added substances (particularly dyes present at low concentrations in a mixture of fuels). Because dyes alone have these shortcomings, a combination of a dye and a marker often is used to tag an organic liquid.
Many commonly used markers are also less than ideal for tagging bulk liquids. Quinizarin and diphenylamine both are fairly sensitive marking materials, with simple detection procedures, but have the disadvantage of poor solubility in nonpolar materials. Their solubility in commonly used petroleum solvents is less than 1%, meaning that an undesirably large volume of a concentrated marker solution must be transported and handled to mark a given volume of fuel. (To encourage rapid and complete dissolution of the marker, it is usually added to the liquid to be marked in the form of a concentrated solution, rather than as a pure compound.)
Furfural has previously been used as a marker for middle distillate fuels. It is extracted by a 10% solution of aniline in acetic acid to form a strongly colored bluish red complex in the lower reagent layer. While quite sensitive, this test has serious disadvantages. First, the slightest contamination of the fuel by residual furfural (which is sometimes used in refining) gives a false positive test. Second, furfural is unstable in certain oils and may not be detectable in such oils after the usual storage period of three to six months. Third, middle distillate fuels tend to discolor appreciably during storage. Some of this discoloration is extracted by aniline acetate and can partially or totally obscure a positive furfural test, particularly if the furfural marked fuel is used to adulterate more expensive or highly taxed unmarked fuel.
As a specific example, furfural has been used in several European countries as a marker for fuel oil at concentrations of 5-10 parts per million (ppm). While certain relatively clean oils give a positive test for as little as 0.5 ppm of furfural, lower quality oils have been observed to give no distinguishable test at concentrations of up to 2 ppm. For such oils the furfural marker cannot be detected in mixtures containing 20%-40% marked fuel. Thus, the less expensive marked fuel can be used in substantial quantities as a diluent without being detected.
Furfural marked fuels have commonly been dyed red, particularly using Solvent Red #19, Solvent Red #24, or related derivatives. But the discoloration previously referred to also obscures the dye, thus preventing visual confirmation that the fuel is tagged.
Recent changes in refining practices further threaten the utility of furfural/red dye combination tagging. In the fairly clean and stable straight run fuels prevalent until recently, furfural is an acceptable marker. But a combination of higher oil prices and sharply increasing demand for diesel fuel as a proportion of the total motive fuel market has necessitated the increasing use of severely cracked heavier grades of crude oil. Severely cracked oils tend to be somewhat unstable, are relatively highly colored when fresh, and tend to destroy the furfural used to mark them. Discoloration and the tendency to destroy the furfural marker both increase as these oils are aged. Tests have shown that 30% to 40% of the furfural is decomposed when it is stored four days in such fuels.
While current practice in many European refineries is production of straight run and cracked fuel oil blends containing 5%-15% cracked product, which will coexist marginally with its furfural marker, it is estimated that the proportion of heavily cracked fuel will exceed 30% in a few years. Under these conditions furfural will be of little or no value as a marker.
The patent literature discloses compounds which are structurally related to the materials disclosed herein as tagging compounds for fuels or other organic liquids. Many of the compounds disclosed herein are novel. The compounds disclosed here which are not novel per se have not been disclosed in the prior art to be useful as a combined dye and marker.
U.S. Pat Nos. 3,764,273 and 3,883,568, the former issued to Turner, et al. on Oct. 9, 1973 and the latter issued to the same inventors on May 13, 1975, disclose 2(2-ethylhexyl)-1,4-dihydroxyanthraquinone: ##STR2## and other substituted anthraquinones in which the depending alkyl moiety has from 1 to 20 carbon atoms, and describes them as being useful as markers for water immiscible organic liquids. But these markers are disclosed to be colorless when employed as markers, and thus do not function both as dyes and as markers at a single concentration.
U.S. Pat. No. 3,192,117, issued to Kaiser, et al. on June 29, 1965; U.S. Pat. No. 3,454,604, issued to Shown et al. on July 8, 1969; U.S. Pat. No. 3,793,349, issued to Johnson, et al. on Feb. 19, 1974; and British Specification No. 1,549,873, published Aug. 8, 1979; respectively disclose the following compounds: ##STR3## (In the latter compound, R is selected from propyl, isopropyl, or ethyl and X is selected from chloride, bromide, cyanide, or 1 to 4 carbon alkoxy. Specific examples of the amino substituent disclosed in the British specification include the following: EQU --NHCH.sub.2 CH.sub.2 OCH.sub.3 ; EQU --NHCH.sub.2 CH.sub.2 CH.sub.2 OCH.sub.3 ; EQU --NHCH.sub.2 CH(CH.sub.3)OCH.sub.3 ; and EQU --NHCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.3.
The compounds disclosed in the four previously listed patents are respectively disclosed to have utility as hair dyes; dyestuffs; blue dyes for polyester fibers; and pigments for transfer printing on polyesters, polyacrylonitriles or paper. None of these compounds are disclosed to be useful as markers or dyes for organic liquids.
U.S. Pat. No. 3,435,054, issued to Kranz, et al. on Mar. 25, 1969; U.S. Pat. No. 3,164,449, issued to Buxbaum on Jan. 5, 1965; and British Specification No. 452,421, published Sept. 17, 1936; disclose structurally related dyes. The dyes disclosed in the U.S. patents are for fuels, and those in the British specification are for cellulose esters and ethers.
Matsuoka, et al., "A Novel 2-Amination of Quinizarin Promoted by Copper Ions," Dyes and Pigments 1:27-37 (1980), teaches synthesis of various 2-amino-1,4 dihydroxyanthraquinones.